The main objective of the research proposed here is to determine whether a "presumptive" neurosecretory system in decapod crustacea, the pericardial organs, can be converted to true endocrine status and whether its products are, in fact, hormones. There is a considerable amount of data on the structure, pharmacology, and biochemistry of this system, but almost none on the physiological role of its secretion and its importance to the organism. The primary questions to be asked are: 1) Is the effect of an active factor now known from isolated assay peparations (cardioexcitation) also seen in intact animals? 2) Can changes in the environment cause changes in the level of circulating active factors or glandular content? 3) Are there effects of glandular extracts in addition to the single one now known? 4) What are the effects of pericardial organ material on specific patterns of motor nerve output. The experimental animal will be the shore crab Carcinus maenas. Techniques used will include monitoring heart rate in situ by means of electrocardiograms, electrophysiological recording of the effects of a presumptive hormone on the activity of specific nerve cells, the extraction and bioassay of active factors contained in the gland and circulatory system after environmental manipulation, and the direct measurement of integumental water permeability in intact crabs and isolated organs.